From Hollywood heart-throb to heart-breaking hobo: Richard Gere will use his celebrity capital this week to raise awareness of homelessness as he arrives in the UK to promote a film in which he plays a man living on the streets.

The actor will meet homeless people who have been helped by leading UK and Irish charities, including Centrepoint and Crisis. He will also make the case for affordable housing and welfare reform in meetings with politicians.

Gere told the Observer: “Most people just think ‘build a shelter, give them a bed for the night’. It really doesn’t solve anything, and quite often creates even more problems.

Gere sat on street corners begging for up to 45 minutes at a time without being recognised, he says. Photograph: Courtesy of Altitude Film Distribution

“Housing is the most important thing in bringing anyone back into society. It’s that sense of self … that ‘I exist and have some importance to people around me’. I’m saddened that we’re all too selfish to help each other as much as we should.”

Gere, now 66, has worked on behalf of the homeless for more than 10 years, playing an active role with New York’s Coalition for the Homeless. He regularly goes to New York shelters in his role as a special inspector for the charity, where he has been moved by the stories of those in need.

Gere recalled that one of the men he met was a costumier: “He said 9/11 happened, he had some mental issues, it all fell apart and he ended up on the streets.”

Another man, a fellow actor, called out to Gere, who had entered the shelter on a visit. “I thought: ‘I’ve been spotted, I have to leave now.’

“He came over to me [saying]: ‘You don’t remember me, do you?’… Whatever his story was, there’s not one of us that has a story that could not lead us to a shelter, to being homeless. Not one of us. So it became quite personal.”

Gere became one of Hollywood’s biggest stars with box-office hits such as An Officer and a Gentleman and Pretty Woman.

His new documentary-style film about homelessness, titled Time Out of Mind, will be released in the UK on Friday4 March. Gere plays a down-and-out man with mental illness who struggles to survive on the streets of New York City, sleeping on benches, eating out of dustbins and begging for spare change. “I’m nobody, I don’t exist,” his character mutters.

The film won the International Critics’ prize at the 2014 Toronto film festival. The New York Times wrote: “Gere is fascinating to observe in this role.”

For the film, Gere, posing as a homeless person, sat at street corners for up to 45 minutes at a time. No one recognised him. “It was bizarre,” he said. “As long as I was in character, I could see people from two blocks away, making a judgment based on how I was dressed. I was very visible to them. People are afraid of being sucked into a black hole of failure and misery. But then it touches something deep in all of us. None of us are that secure that it couldn’t be us also.”

Richard Gere in Time out of Mind, a film about homelessness and mental illness. Photograph: Altitude Film Distribution

Making the film with director Oren Moverman, whose movies include the Oscar-nominated military drama The Messenger, Gere said he felt an “enormous responsibility to tell the truth”.

Jon Sparkes, chief executive of Crisis, said that the film “certainly does justice to the issue”.

“It portrays the reality. It’s not a celebrity playing a homeless person. It’s a film about a homeless person,” he said.

Seyi Obakin, chief executive of Centrepoint, said: “There are 83,000 homeless young people in the UK and the scale of the problem is such that it can sometimes take an individual of Richard Gere’s international renown to bring the issue the attention it deserves.”

Gere said: “I’ve been living in New York since I was 20. We all have our homeless people on our block. Then they disappear and who knows what happens to them. It’s a wide variety of issues. It’s not just mental illness … But people tend to be seen monolithically. That’s one of the failures of the social services, where people think one size fits all. There’s an infinite number of stories that lead people to being on the street.”

While some argue against giving money to homeless people in case they spend it on drugs and alcohol, he said: “It’s not to up to us to make that judgment. Give them money. Ultimately, a genuine act of generosity communicates to that person.”

Altitude Films, which is distributing the movie, will donate 10% of the UK profits from Time Out of Mind to Crisis and Centrepoint.